The use of wind turbines to harness wind energy in order to generate electrical power represents an essential part of incorporating renewable energies in the energy-mix. A typical wind turbine is known from U.S. Pat. No. 7,431,567 B1 comprising a tower with a first cavity, a turret pivotably attached to the tower with a second cavity, a spindle attached to the turret with a third cavity, a wind rotor hub rotatably attached to the spindle with a fourth cavity, with the cavities communicating with one another such that an average-size man can move through the cavities.
Maintenance of such wind turbines is a considerable factor in the total cost and effort of any project. Heavy components in a wind turbine such as yaw motors, hydraulic or brake components, etc. are typically handled or replaced due to mal-function or age for instance. Therefore, external cranes and hoist mechanisms are used when a wind turbine is undergoing service inspection or repair. Such cranes are large and bulky, so that they are not sufficiently efficient for lowering the parts from the nacelle frame of the wind turbine and hoisting them back to the nacelle frame. Besides, these cranes are expensive so that only a small number of the cranes are available for each wind turbine having parts to be handled.
Attempts for overcoming such problems have been proposed consisting in providing a crane fixed or detachably installed inside a nacelle frame.
EP 1 291 521 A1 refers to a wind turbine whereby the nacelle is provided with an overhead frame from which the generator is suspended and doors at the bottom of the nacelle.
EP 1 101 934 A2 depicts a wind turbine having a movable on-board crane on a mounting, which has a load receiver. The mounting can move along the machinery casing, carrying e.g. the generator or the transmission. There is an aperture in the bottom of the machinery casing part projecting radially from the tower.
US 2007/0200103 A1 refers to a wind turbine with a nacelle frame and a first hoist permanently mounted to the frame being movable along the nacelle frame by use of wheels or rails. The first hoist is adapted to hoist a second, more powerful hoist and crane on the frame, with the second hoist and the crane being removably mounted on the nacelle frame as well. Further, by using the second hoist and the crane, a winch is hoisted on the frame and removably mounted to it.
The systems known from prior art are either not flexible in terms of degrees of freedom of movement of heavy components within the nacelle or the upper part of the wind turbine in general or relatively complicated regarding their assembly.